This invention is drawn to the field of heat exchangers and more particularly to an electrohydrodynamic (EHD) inductively pumped heat pipe.
A conventional heat pipe is a two phase self-contained heat exchanger that transfers heat energy from a boiling section to a condensing section by means of supplying heat energy to a working fluid which, in evaporating and expanding into gas phase at the evaporator, carries in the form of the latent heat of vaporization the supplied heat to the condensor. Heat is removed by the condensor in the condensation of the gas back into liquid phase. A wick or matrix of capillary webbing establishes a capillary pumping head which returns the liquid condensate from the condensing section to the evaporating section by means of surface tension, and the cycle is repeated. This process continues indefinitely in the absence of other forces and results in a heat transfer rate substantially greater than the heat transfer rate of homogeneous metallic conductors.
The heat transfer rate of heat pipes is limited to a maximum thermal throughput often set by an upper limit on the capacity of the capillary head to pump the liquid condensate from the condensor to the evaporator. This upper limit is especially restrictive in medium and low temperature applications, where the use of dielectric working fluids having low surface tension and low thermal conductivity provide a comparatively weak capillary pumping head. In such situations, the evaporator may burn out due to a failure of the capillary pumping head to provide a sufficient quantity of working fluid to the evaporator.
Specially designed composite wicks having capillary driven low resistance longitudinal arteries and electrohydrodynamic flow structures have been used in an effort to augment the comparatively low maximum thermal throughput of low and medium temperature heat pipes. The principal difficulty with the composite wicks has been a considerable loss in performance due to entrapped gas occlusions which form in the artieries as a result of, among other factors, unsuccessful priming. The occlusions impede the return flow of the liquid condensate and lead to evaporator burnout.
Known electrohydrodynamic (EHD) heat pipes utilize the electrostatic pressure exerted on a dielectric working fluid by axial rod electrodes. The electrodes, raised to high voltage, form tent-like low resistance return flow channels which pump the working fluid from the condensing to the evaporating sections. The maximum electrostatic pressure that can be exerted by the axial electrode structure to pump the liquid condensate is limited, however, by the breakdown strength of the working fluid which restricts the maximum thermal throughput of this type of EHD heat pipe.